The general hypothesis to be tested by this proposed research plan is that low-pressure baroreceptors of the cardiovascular system located in the right heart, liver, kidneys, spleen and mesenteric beds cotribute to the overall neural control of the circulation. The specific aims to be studied in anesthetized dogs are to determine: 1) the location and physiological characteristics of the low-pressure baroreceptors; 2) the reflex effects of low-pressure baroreceptors on sympathetic and vagal efferent nerve activity to the heart, liver, kidney, spleen, mesenteric bed and hindlimb; 3) the cardiac reflex effects, by measuring heart rate, artrial pacemaker shifts and contractile force; 4) the reflex effects on systemic blood pressure and volume; 5) reflex changes in vascular resistance and volume in selected organ beds such as the kidney, spleen and hindlimb; 6) if there is a heirarchy of low-pressure baroreceptor reflex effects and the conditions under which they occur. Although a number of studies have given ample evidence to substantiate the existence of low-pressure baroreceptors, their precise role inthe neural control of the circulation remains to be explored. The importance of low-pressure baroreceptors in clinically relevant pathological conditions such as congestive heart failure, cardiac tamponade, orthostatic hypotension, cirrhosis of the liver, portal hypertension, spinal anesthesia, hemorrhage, shock and hypertension remains unknown. The proposed research should provide a base of knowledge about the reflex role of these low-pressure baroreceptors in the normal animal, so that the contribution of these reflexes to irreversible complications of these disorders could be evaluated in pathological models. Ultimately, these studies could lead to the implementation of new therapeutic strategies for the treatment of patients with congestive heart failure, and other disorders which alter normal circulatory function.